C＃需要构造函数语法解释 [英] C# Constructor syntax explanation needed

问题描述

有人可以向我解释下面的构造函数语法。我以前没有遇到它，并在同事的代码中注意到。

  public Service（）：this（Service.DoStuff（），DoMoreStuff（））
 {} 
  

解决方案

它链接到同一类中的另一个构造函数。基本上任何构造函数都可以使用：this（...），或链接到同一类中的另一个构造函数，到基本类中使用：base（...）的构造函数。如果你没有，它相当于：base（）。

链接的构造函数被执行<

之前 实例变量初始值设定项已经执行。 http://pobox.com/~skeet/csharp/constructors.html\"> my article on constructor chaining or the

例如，考虑下面的代码：

 使用System; 
 
 public class BaseClass 
 {
 public BaseClass（s​​tring x，int y）
 {
 Console.WriteLine（Base class constructor）; 
 Console.WriteLine（x = {0}，y = {1}，x，y）; 
} 
} 
 
 public class DerivedClass：BaseClass 
 {
 //链接到1参数构造函数
 public DerivedClass（）：这个（Foo）
 {
 Console.WriteLine（Derived class parameterless）; 
} 
 
 public DerivedClass（s​​tring text）：base（text，text.Length）
 {
 Console.WriteLine（Derived class with parameter）; 
} 
 
} 
 
 static class Test 
 {
 static void Main（）
 {
 new DerivedClass （）; 
} 
} 
  

主方法调用 DerivedClass 中的无参参数构造函数。它链接到 DerivedClass 中的单参数构造函数，然后它链接到 BaseClass 中的双参数构造函数。当该基础构造函数完成时， DerivedClass 中的单参数构造函数继续，然后当完成时，原始的无参构造函数继续。所以输出是：

 基类构造函数
x = Foo，y = 3 
 
派生类无参数
  

Can someone please explain the following constructor syntax to me. I haven't come across it before and noticed it in a colleagues code.

public Service () : this (Service.DoStuff(), DoMoreStuff())
{ }

解决方案

It chains to another constructor in the same class. Basically any constructor can either chain to another constructor in the same class using : this (...), or to a constructor in the base class using : base(...). If you don't have either, it's equivalent to : base().

The chained constructor is executed after instance variable initializers have been executed, but before the body of the constructor.

See my article on constructor chaining or the MSDN topic on C# constructors for more information.

As an example, consider this code:

using System;

public class BaseClass
{
    public BaseClass(string x, int y)
    {
        Console.WriteLine("Base class constructor");
        Console.WriteLine("x={0}, y={1}", x, y);
    }
}

public class DerivedClass : BaseClass
{
    // Chains to the 1-parameter constructor
    public DerivedClass() : this("Foo")
    {
        Console.WriteLine("Derived class parameterless");
    }

    public DerivedClass(string text) : base(text, text.Length)
    {
        Console.WriteLine("Derived class with parameter");
    }

}

static class Test
{
    static void Main()
    {
        new DerivedClass();
    } 
}

The Main method calls the parameterless constructor in DerivedClass. That chains to the one-parameter constructor in DerivedClass, which then chains to the two-parameter constructor in BaseClass. When that base constructor completes, the one-parameter constructor in DerivedClass continues, then when that finishes, the original parameterless constructor continues. So the output is:

Base class constructor
x=Foo, y=3
Derived class with parameter
Derived class parameterless

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